Image forming apparatus

Abstract

An image forming apparatus includes a controller and multiple image forming units each of which includes an image bearer, a toner image forming device to form a toner image on the image bearer, a transfer device to transfer the toner image from the image bearer onto a transfer medium, a cleaning device to remove toner from a surface of the image bearer, a waste-toner tube through which toner removed by the cleaning device is transported, and a toner conveying member to transport toner by rotation and disposed inside the waste-toner tube. The controller changes a rotation speed of the toner conveying member for each of the multiple image forming units according to toner type including a first toner and a second toner having poorer flow properties than the first toner, and at least one image forming units uses the second toner and the rest use the first toner.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 multiple image forming units each of which includes:
 an image bearer; 
 a toner image forming device to form a toner image on the image bearer; 
 a transfer device to transfer the toner image from the image bearer onto a transfer medium; 
 a cleaning device to remove toner from a surface of the image bearer from which the toner image is transferred; 
 a waste-toner tube through which toner removed by the cleaning device is transported; 
 a toner conveyor to transport toner by rotation, the toner conveyor disposed inside the waste-toner tube; and 
 
 a controller to change a rotation speed of the toner conveyor for each of the multiple image forming units according to toner type including a first toner and a second toner having poorer flow properties than the first toner, 
 wherein at least one of the multiple image forming units uses the second toner and the remaining image forming units use the first toner. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein the controller sets the rotation speed of the toner conveyor to an increased speed when a toner-related variable contributing to an increase in amount of toner removed by the cleaning device exceeds a threshold level. 
     
     
       3. The image forming apparatus according to  claim 2 , wherein the toner-related variable comprises an image area ratio of the toner image on the image bearer. 
     
     
       4. The image forming apparatus according to  claim 2 , wherein the toner-related variable comprises a setting of toner adhesion amount to the image bearer determined by the controller. 
     
     
       5. The image forming apparatus according to  claim 1 , wherein the controller widens a sheet interval area on the image bearer according to the toner type used in the image forming unit during continuous image formation in which images are successively formed on multiple number of sheets of recording media. 
     
     
       6. The image forming apparatus according to  claim 5 , wherein, when a toner-related variable contributing to an increase in amount of toner removed by the cleaning device exceeds a threshold level, the controller widens the sheet interval area according to the toner type used in the image forming unit. 
     
     
       7. The image forming apparatus according to  claim 6 , wherein the toner-related variable comprises an image area ratio of the toner image on the image bearer. 
     
     
       8. The image forming apparatus according to  claim 6 , wherein the toner-related variable comprises a setting of toner adhesion amount to the image bearer determined by the controller. 
     
     
       9. The image forming apparatus according to  claim 1 , further comprising:
 a downstream conveyance tube positioned downstream from the waste-toner tube; and 
 a downstream toner conveyor to transport toner by rotation, the downstream toner conveyor disposed inside the downstream conveyance tube, 
 wherein the controller sets a rotation speed of the downstream toner conveyor to an increased speed according to the toner type for each of the multiple image forming units. 
 
     
     
       10. The image forming apparatus according to  claim 9 , wherein the controller determines the rotation speed of the downstream toner conveyor according to a toner-related variable that contributes to an increase in amount of toner removed by the cleaning device. 
     
     
       11. The image forming apparatus according to  claim 10 , wherein the toner-related variable comprises an image area ratio of the toner image on the image bearer. 
     
     
       12. The image forming apparatus according to  claim 10 , wherein the toner-related variable comprises a setting of toner adhesion amount to the image bearer determined by the controller. 
     
     
       13. The image forming apparatus according to  claim 1 , wherein the toner type comprises polymerization toner and pulverized toner. 
     
     
       14. The image forming apparatus according to  claim 1 , wherein the toner type comprises colored toner and transparent toner. 
     
     
       15. The image forming apparatus according to  claim 1 , wherein the cleaning device comprises a lubricant applicator to apply lubricant onto the surface of the image bearer,
 each of the multiple image forming units further comprises a driving source to drive both of the lubricant applicator and the toner conveyor, and 
 the controller sets a speed of the driving source of the cleaning device of the at least one of the multiple image forming units using the second toner to an increased speed from a speed of the driving source of the cleaning device of the image forming unit using the first toner. 
 
     
     
       16. The image forming apparatus according to  claim 15 , further comprising a humidity detector to detect absolute humidity in an environment in which the image forming apparatus is installed,
 wherein, when a speed for lubrication refers to a speed of the driving source to maintain lubrication by the lubricant applicator and a speed for transport of toner refers to a speed of the driving source to maintain transport of toner by the toner conveyor, the controller sets the speed of the driving source of the cleaning device of the at least one of the multiple image forming units using the second toner to the increased speed when the absolute humidity detected by the humidity detector is in a first range in which the speed for lubrication is lower than the speed for transport of toner in the at least one of the multiple image forming units using the second toner. 
 
     
     
       17. The image forming apparatus according to  claim 16 , wherein, when the absolute humidity detected by the humidity detector is in the first range, the controller sets the speed of the driving source of the cleaning device of the at least one of the multiple image forming units using the second toner to the speed for transport of toner. 
     
     
       18. An image forming apparatus comprising:
 multiple image forming units each of which includes:
 an image bearer; 
 a toner image forming device to form a toner image on the image bearer; 
 a transfer device to transfer the toner image from the image bearer onto a transfer medium; 
 a cleaning device to remove toner from a surface of the image bearer from which the toner image is transferred, 
 the cleaning device including a lubricant application roller to apply lubricant onto the surface of the image bearer and a driving source to drive both of the lubricant applicator and the toner conveyor; 
 a waste-toner tube through which toner removed by the cleaning device is transported; and 
 a toner conveyor to transport toner by rotation, the toner conveyor disposed inside the waste-toner tube, 
 
 wherein at least one of the multiple image forming units uses a second toner having poorer flow properties than a first toner used in the remaining image forming units, and 
 the controller sets a speed of the driving source of the cleaning device of the at least one of the multiple image forming units using the second toner to an increased speed from a speed of the driving source of the cleaning device of the image forming unit using the first toner. 
 
     
     
       19. An image forming apparatus comprising:
 multiple image forming units each of which includes:
 an image bearer, 
 a toner image forming device configured to form a toner image on the image bearer; 
 a transfer device configured to transfer the toner image from the image bearer onto a transfer medium, and 
 a cleaning device configured to remove toner from a surface of the image bearer from which the toner image is transferred; 
 a first toner conveyor configured to transport a first toner at a first rotational speed; and 
 a second toner conveyor configured to transport a second toner at a second rotational speed, different from the first rotational speed, the second toner having poorer flow properties than the first toner, 
 wherein at least one of the multiple image forming units uses the second toner and the remaining image forming units use the first toner. 
 
 
     
     
       20. The image forming apparatus according to  claim 19 , wherein at least one of the first and second toner conveyors is a component of at least one of the multiple image forming units.